linux-kernel - Re: [PATCH v2] pwm-backlight: allow for non-increasing brightness levels

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Message-ID: <526191C5.7060705@newsguy.com>
Date:	Fri, 18 Oct 2013 12:53:41 -0700
From:	Mike Dunn <mikedunn@...sguy.com>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Richard Purdie <rpurdie@...ys.net>,
	Jingoo Han <jg1.han@...sung.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	linux-pwm@...r.kernel.org, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v2] pwm-backlight: allow for non-increasing brightness
 levels

On 10/18/2013 12:46 AM, Thierry Reding wrote:
> On Sun, Sep 22, 2013 at 09:59:56AM -0700, Mike Dunn wrote:
>> Currently the driver assumes that the values specified in the
>> brightness-levels device tree property increase as they are parsed from
>> left to right.  But boards that invert the signal between the PWM output
>> and the backlight will need to specify decreasing brightness-levels.
>> This patch removes the assumption that the last element of the array is
>> the maximum value, and instead searches the array for the maximum value
>> and uses that in the duty cycle calculation.
>>
>> Signed-off-by: Mike Dunn <mikedunn@...sguy.com>
>> ---
>> Changelog:
>> v2: 
>> - commit message reworded; correct line wrap used
>> - 'max_level' variable renamed to 'scale'
>> - loop counter variable type changed to unsigned int
>> - value held in scale changed from array index to actual maximum level
>> - blank lines added around loop for readability
>>
>>  drivers/video/backlight/pwm_bl.c | 12 ++++++++++--
>>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> Hey Mike,
> 
> I've pushed a slightly different version of this patch which gets rid of
> the intermediate max variable and uses the new scale field exclusively
> to pass the same information around. Could you look at the patch from my
> for-next branch in the PWM tree and see whether that still works for the
> specific hardware that you need this for?


Yes looks good.

I also tested the current HEAD of for-next on the Palm Treo 680, including the
enable-gpios DT node property.  I will have to do more work and investigation
before I will be able to try the power-supply property, though.

Thanks,
Mike

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